Seven BBRI scientists working in fields in which protein interactions are a primary component, propose to purchase a Stroboscopic Time-Resolved Spectrofluorometer which will enable fluorescence and phosphorescence lifetime measurements from nanoseconds to seconds, anisotropy decay and steady-state photon counting spectral measurements. The instrument will enable study of the emission of intrinsic and extrinsic probes of protein structure and interactions and provide information about the accessibility, environment, and flexibility of the domain to which the probe is attached. In addition, measurements of distance, distance distributions, and distance changes via FRET and LRET (Forster and fluorescence resonance energy transfer, respectively) will be enabled. Sensitive measurements of binding profiles will allow binding constants and stoichiometry and thermal dependence of fluorescence parameters to be obtained. This instrument will facilitate the current experimental approaches of the investigators which include, X-ray crystallography, fluorescence and phosphorescence spectroscopy, differential scanning and isothermal titration calorimetry, circular dichroism, mass spectroscopy and other biochemical / biophysical measurements. The time-resolved spectrofluometer will complement NIH funded structural and functional studies focused on understanding the regulation of smooth, cardiac and skeletal muscle, the function of chaperones, proteins involved in excitation-contraction coupling in skeletal and cardiac muscle and proteins involved in anthrax infection. These studies will provide the basis for understanding the diseased state including cardiac and skeletal myopathies, hypertension, atherosclerosis, and viral infection.